Aliphatic alcohols occur
naturally in free form but more usually in esterified or etherified form.
Surfactants are frequently derived from fatty alcohols like fatty alcohol
sulfates, ethoxylates, and alkyl polyglycosides.
The analysis of long-chain alcohols in vegetable extracts, such as policosanols,
is done after saponification, by preparative TLC and GLC. We give below a brief
description of the efficient procedure used for the analysis of policosanol from
peanut oil (Cherif AO et al., J Agric Food Chem 2010, 58, 12143).

Saponification : mix 5 g of oil with 50 ml of ethanolic KOH 12%(w/v)
solution. The mixture is heated at 60°C for 1.30 h. After cooling, 50 ml of
water are added to the mixture. The unsaponifiable matter is extracted four
times with 50 ml of petroleum ether which is washed with 50 ml of ethanol/water
(1:1) (v/v). The lipid fraction is dried under nitrogen, dissolved in chloroform
and analyzed by TLC.TLC : alcohols are separated into sub-fractions using one-dimensional TLC
with hexane/ethanol (65:35,v/v). After development, the plates are sprayed with
primuline and viewed under UV light. Bands corresponding to aliphatic alcohols
are scraped off separately and extracted three times with chloroform/ethanol
(1:1).Derivatization and analysis : aliphatic alcohols are mixed with 80 ml
of N,O-bis(trimethylsilyl) trifluoroacetamide and 20 ml
of chlorotrimethylsilane. The mixture is vortexed and heated at 60°C for 30
min. After silylation, the solution was then directly injected to the gas
chromatograph.

Sensitive techniques are often
needed to evaluate their amounts in the environment or in biological samples.
Thus, we give below a procedure based on a simple chemical derivatization which
allows a high detection sensitivity (Meissner C et al., Chromatographia 1999,
49, 7).

Derivatization
: To 860 ml
dry acetonitrile 100 ml
fatty alcohol and 40 ml
methylimidazole catalyst were added. 1 ml carbazole-9-carbonyl chloride solution
(4 mg/ml) was added to the mixture. The reaction time was 30 min at 65°C.
The reaction mixture was purified from excess reagent by filtration through a RP
18 SPE cartridge conditioned with 2 ml methanol and 2 ml acetonitrile/water
(60/40, v/v). The cartridge was washed with 12 ml of acetonitrile/water
(60/40, v/v), air-dried for 10 min and eluted with 2 ml diethyl ether. After
removing ether under a nitrogen flow the residue is dissolved in 1 ml
acetonitrile. The derivatives were stable for more than 24 h in solution.
Fatty alcohol ethoxylates were derivatized according to the same procedure.

Separation

Acetonitrile
was pumped at a flow rate of 1.5 ml/min.
The excitation wavelength was 228 nm and emission was measured at 318 nm.
An example of trace analysis of fatty alcohols (injection of 200 ml of 10 nM
standards from 12 to 18 carbon atoms) is given below.